Mix together butter and brown sugar. Add egg, vanilla, baking soda and cream of tartar. Mix well. Stir in flour. Cover bowl and chill dough in refrigerator for one hour. Roll dough into one inch balls. Roll balls in the cinnamon sugar mixture. Place balls about two inches apart on a greased (or parchment papered) cookie sheet. Bake at 350° for 10 minutes or until the cookies are golden brown.